206 research outputs found
Magnetic frustration in an iron based Cairo pentagonal lattice
The Fe3+ lattice in the Bi2Fe4O9 compound is found to materialize the first
analogue of a magnetic pentagonal lattice. Due to its odd number of bonds per
elemental brick, this lattice, subject to first neighbor antiferromagnetic
interactions, is prone to geometric frustration. The Bi2Fe4O9 magnetic
properties have been investigated by macroscopic magnetic measurements and
neutron diffraction. The observed non-collinear magnetic arrangement is related
to the one stabilized on a perfect tiling as obtained from a mean field
analysis with direct space magnetic configurations calculations. The
peculiarity of this structure arises from the complex connectivity of the
pentagonal lattice, a novel feature compared to the well-known case of
triangle-based lattices
Calibration of ac and dc magnetometers with a Dy2O3 standard
This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.The ac susceptibility and magnetization curves of a glued Dy2O3 powder sample are measured by an ac susceptometer and a dc superconducting quantum interference device magnetometer, both of which have been calibrated previously. It is shown that the magnetic moment of the paramagnetic sample as a function of field and temperature may be accurately expressed by a combination of the Curie-Weiss law and the Langevin function at T > 45 K with three adjusting parameters, so that the dc magnetization curves and the magnitude and phase of ac susceptibility at different values of dc bias field measured by any magnetometer can be calibrated by using Dy2O3 as a standard. The expressions are empirical and cannot be justified in the entire field and temperature range by existing theories of paramagnetism. Below 10 K, indication of approaching a possible phase transition is found. It is shown that pure Dy2O3 powder may be used as a primary standard, with susceptibility [13.28(T + 17)]−1 emu/Oe/g at T > 50 K and H < 10 kOe, in consistency with the Curie-Weiss law and the quantum mechanical theory of paramagnetism
Calibration of low-temperature ac susceptometers with a copper cylinder standard
This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.A high-quality low-temperature ac susceptometer is calibrated by comparing the measured ac susceptibility of a copper cylinder with its eddy-current ac susceptibility accurately calculated. Different from conventional calibration techniques that compare the measured results with the known property of a standard sample at certain fixed temperature T, field amplitude Hm, and frequency f, to get a magnitude correction factor, here, the electromagnetic properties of the copper cylinder are unknown and are determined during the calibration of the ac susceptometer in the entire T, Hm, and f range. It is shown that the maximum magnitude error and the maximum phase error of the susceptometer are less than 0.7% and 0.3°, respectively, in the region T = 5-300 K and f = 111-1111 Hz at Hm = 800 A/m, after a magnitude correction by a constant factor as done in a conventional calibration. However, the magnitude and phase errors can reach 2% and 4.3° at 10 000 and 11 Hz, respectively. Since the errors are reproducible, a large portion of them may be further corrected after a calibration, the procedure for which is given. Conceptual discussions concerning the error sources, comparison with other calibration methods, and applications of ac susceptibility techniques are presented
Electric field control of exchange bias in multiferroic epitaxial heterostructures
The magnetic exchange bias between epitaxial thin films of the multiferroic
(antiferromagnetic and ferroelectric) hexagonal YMnO3 oxide and a soft
ferromagnetic (FM) layer is used to couple the magnetic response of the
ferromagnetic layer to the magnetic state of the antiferromagnetic one. We will
show that biasing the ferroelectric YMnO3 layer by an appropriate electric
field allows modifying and controlling the magnetic exchange bias and
subsequently the magnetotransport properties of the FM layer. This finding may
contribute to pave the way towards a new generation of electric-field
controlled spintronics devices.Comment: 15 pages, 5 figures, submitte
Phonon and magnon scattering of antiferromagnetic Bi2Fe4O9
The phonon structure of antiferromagnetic Bi2Fe4O9 (space group Pbnm No. 55, TN≈240  K) was studied theoretically by calculations of lattice dynamics and experimentally between 10 and 300 K by polarized Raman spectroscopy. Most of the 12Ag+12B1g+9B2g+9B3g Raman modes were unambiguously identified. Strong second-order scattering was observed for ab-plane-confined incident and scattered light polarizations. In addition to the phonon-scattering, broad Raman bands with typical characteristics of magnon scattering appear below TN. The magnon bands are analyzed on the basis of magnetic structure of Bi2Fe4O9 and attributed to two- magnon excitations
Electric field effects on magnetotransport properties of multiferroic Py/YMnO3/Pt heterostructures
We report on the exchange bias between antiferromagnetic and ferroelectric
hexagonal YMnO3 epitaxial thin films sandwiched between a metallic electrode
(Pt) and a soft ferromagnetic layer (Py). Anisotropic magnetoresistance
measurements are performed to monitor the presence of an exchange bias field.
When the heteroestructure is biased by an electric field, it turns out that the
exchange bias field is suppressed. We discuss the dependence of the observed
effect on the amplitude and polarity of the electric field. Particular
attention is devoted to the role of current leakage across the ferroelectric
layer.Comment: Accepted for publication in Philosophical Magazine Letters (Special
issue on multiferroics
Magnetization Reversal by Electric-Field Decoupling of Magnetic and Ferroelectric Domains Walls in Multiferroic-Based Heterostructures
We demonstrate that the magnetization of a ferromagnet in contact with an
antiferromagnetic multiferroic (LuMnO3) can be speedily reversed by electric
field pulsing, and the sign of the magnetic exchange bias can switch and
recover isothermally. As LuMnO3 is not ferroelastic, our data conclusively show
that this switching is not mediated by strain effects but is a unique
electric-field driven decoupling of the ferroelectric and ferromagnetic domains
walls. Their distinct dynamics are essential for the observed magnetic
switching
Strain-driven non-collinear magnetic ordering in orthorhombic epitaxial YMnO3 thin films
We show that using epitaxial strain and chemical pressure in orthorhombic
YMnO3 and Co-substituted (YMn0.95Co0.05O3) thin films, a ferromagnetic response
can be gradually introduced and tuned. These results, together with the
measured anisotropy of the magnetic response, indicate that the unexpected
observation of ferromagnetism in orthorhombic o-RMnO3 (R= Y, Ho, Tb, etc) films
originates from strain-driven breaking of the fully compensated magnetic
ordering by pushing magnetic moments away from the antiferromagnetic [010]
axis. We show that the resulting canting angle and the subsequent ferromagnetic
response, gradually increase (up to ~ 1.2\degree) by compression of the unit
cell. We will discuss the relevance of these findings, in connection to the
magnetoelectric response of orthorhombic manganites.Comment: Text + Figs Accepted in J. Appl. Phy
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